System.NullRefe renceException in unmanaged/managed interop

[Yoni Rabinovitch]

Hi,

I am new to C#, so I apologise if this is a stupid question.

I have some 3rd party C++ code, which gets built as static libraries
(not DLLs).

I want to create a C# form, which will call the C++ code.

So, I understand that I need to create a Managed C++ Wrapper, for any
C++ classes that I want to call from C#.

I have created a Managed C++ DLL, which links with my C++ static
libraries.

The Managed C++ DLL contains a "wrapper" class, defined as follows:
=============== =============== =============== =============== ===========
// AppsEMSWrapper_ Take1.h

#pragma once

// ModelInterface is the C++ class we are wrapping
#include <ModelInterface .h>

using namespace System;

namespace AppsEMSWrapper_ Take1
{
public __gc class ModelInterfaceW rapper {
public:
ModelInterfaceW rapper();
void modelMainEntryP ointWrapper(int RunAsLCT);
private:
ModelInterface __nogc* m_pModelInterfa ce;
};

}
=============== =============== =============== =============== ============
// This is the main DLL file.

#include "stdafx.h"

#include "AppsEMSWrapper _Take1.h"

using namespace AppsEMSWrapper_ Take1;

ModelInterfaceW rapper::ModelIn terfaceWrapper( )
{
m_pModelInterfa ce = new ModelInterface( );
}

void ModelInterfaceW rapper::modelMa inEntryPointWra pper(int RunAsLCT)
{
m_pModelInterfa ce->modelMainEntry Point(RunAsLCT) ;
}

=============== =============== =============== =============== ===========

Now, my C++ code uses static variables, and so I am following the
instructions in the MSDN article entitled:
"Converting Managed Extensions for C++ Projects from Pure Intermediate
Language to Mixed Mode".

With regards to "Modifying Components That Consume the DLL for Manual
Initializiation " as described in that article, I think I need to
follow the instructions under the bullet which reads:
"Your DLL's consumers can use managed code, and your DLL contains
either DLL exports or managed entry points."

So, I added the ManagedWrapper. cpp file to my managed DLL,as described
in the article.

Then, my C# code is shown below:
=============== =============== =============== =============== ===========
using System;
using AppsEMSWrapper_ Take1;

namespace ConsoleApplicat ion1
{
/// <summary>
/// Summary description for Class1.
/// </summary>
class Class1
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main(string[] args)
{

Console.WriteLi ne("Start Rose RT model ...");

ManagedWrapper. minitialize();

ModelInterfaceW rapper miw = new ModelInterfaceW rapper();

miw.modelMainEn tryPointWrapper (1);

ManagedWrapper. mterminate();

}
}
}
=============== =============== =============== =============== =============== ====

Now, with all this I am able to build my application. However, I get:

An unhandled exception of type 'System.NullRef erenceException '
occurred in appsemswrapper_ take1.dll

Additional information: Object reference not set to an instance of an
object.

The call stack is:

appsemswrapper_ take1.dll!AppsE MSWrapper_Take1 .ModelInterface Wrapper.modelMa inEntryPointWra pper(__int32
RunAsLCT = 0x1) Line 17 C++
ConsoleApplicat ion1.exe!Consol eApplication1.C lass1.Main(stri ng[] args
= {Length=0x0}) Line 26 C#
Note that I have tried compiling all my C++ libraries with /clr. I
still get the same exception, although the call stack is different
(with /clr, I seem to manage to get into the C++ code at least, though
not very far).

What am I doing wrong ??? Please help !!!

Thanks !!!